It has been apparent for sometime that valuable items of metal are being wasted by being discarded with other waste material, and in this category of metal items that fraction made up of aluminum is not susceptible of easy recovery as is the ferrous type which responds to magnetic separators. It is recognized that aluminum used in containers is an especially valuable source of that metal which if recoverable can be recycled so as to reduce the amount of energy related treatment for processing bauxite that is needed in the manufacture of aluminum used in the manufacture of containers.
The recovery of metal from waste material has been disclosed by Vollmer in U.S. Pat. No. 2,844,184 of July 22, 1958; by Anderson et al in U.S. Pat. No. 2,942,792 of June 28, 1960; by Williams in U.S. Pat. No. 3,283,698 of Nov. 8, 1966; and further by Williams in U.S. Pat. No. 3,702,682 of Nov. 14, 1972. The main purpose for the apparatus of the prior art has been focused on the recovery of magnetic material, or in the case of the Anderson disclosure of the sorting of aluminum scrap from other metals by a method calling for gravity separation thereof in a water suspension to recover light metal portions from scrap material and melting the recovered light metal by a so called "sweating process" in which an attempt is made to selectively melt the aluminum away from metallic contamination still mixed therewith. By and large, recovery apparatus has operated on the premise that magnetically responsive waste material is economically extracted from a moving stream by passing it adjacent magnetic separating devices and allowing the non-magnetic waste to pass on by. More recently apparatus specifically arranged to recover the aluminum fractions in metallic waste is disclosed in the application of Williams et al, Ser. No. 083,573 filed Oct. 11, 1979.
Other prior art apparatus is directed toward means for permitting the material shredder to either recirculate material or throw out hard to shred material, and cooperating means to direct the hard to shred material out of the shredding chamber. This prior art is represented by Knoblock U.S. Pat. No. 1,104,121 of July 21, 1914; Lykken et al U.S. Pat. No. 2,931,581 of Apr. 5, 1960; Gruendler U.S. Pat. No. 2,491,661 of Dec. 20, 1949; Gondard U.S. Pat. No. 3,082,963 of Mar. 26, 1963; and Meyer U.S. Pat. No. 3,442,458 of May 6, 1969.
The disposal of waste materials of all kinds and description in the past have been carried out by dumping in landfill areas and allowing destruction thereof by natural processes. The landfill disposal has worked in a satisfactory manner for materials that will disintegrate in time. That disposal operation does not take into account the fact that metals are slow to disintegrate, and that aluminum does not disintegrate and is therefore a troublesome component of waste. Landfill disposal operations are fast being shut down because it is recognized that a high proportion of the waste material contains heat values, that the ferrous metals can be reused, and the aluminum is a valuable source of that metal for recycling processes. However, these metals are reduced in value if iron or ferrous material contaminates the aluminum, or if aluminum contaminates the iron or ferrous material. The contamination of these metals is a problem with bimetal containers where ferrous and aluminum parts are used together.